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Message-Id: <20201221130754.12628-1-weichen.chen@linux.alibaba.com>
Date: Mon, 21 Dec 2020 21:07:44 +0800
From: weichenchen <weichen.chen@...ux.alibaba.com>
To: kuba@...nel.org
Cc: splendidsky.cwc@...baba-inc.com, yanxu.zw@...baba-inc.com,
weichenchen <weichen.chen@...ux.alibaba.com>,
"David S. Miller" <davem@...emloft.net>,
Hangbin Liu <liuhangbin@...il.com>,
David Ahern <dsahern@...nel.org>,
Roopa Prabhu <roopa@...ulusnetworks.com>,
Roman Mashak <mrv@...atatu.com>,
Vasily Averin <vvs@...tuozzo.com>,
Jeff Dike <jdike@...mai.com>,
Li RongQing <lirongqing@...du.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v2] net: neighbor: fix a crash caused by mod zero
pneigh_enqueue() tries to obtain a random delay by mod
NEIGH_VAR(p, PROXY_DELAY). However, NEIGH_VAR(p, PROXY_DELAY)
migth be zero at that point because someone could write zero
to /proc/sys/net/ipv4/neigh/[device]/proxy_delay after the
callers check it.
This patch double-checks NEIGH_VAR(p, PROXY_DELAY) in
pneigh_enqueue() to ensure not to take zero as modulus.
Signed-off-by: weichenchen <weichen.chen@...ux.alibaba.com>
---
V2:
- Use READ_ONCE() to prevent the complier from re-reading
NEIGH_VAR(p, PROXY_DELAY).
- Give a hint to the complier that delay <= 0 is unlikely
to happen.
Note: I don't think having the caller pass in the value is a
good idea mainly because delay should be only decided by
/proc/sys/net/ipv4/neigh/[device]/proxy_delay rather than the
caller.
---
net/core/neighbour.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 9500d28a43b0..7b03d3f129c0 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1570,9 +1570,14 @@ void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p,
struct sk_buff *skb)
{
unsigned long now = jiffies;
+ unsigned long sched_next;
- unsigned long sched_next = now + (prandom_u32() %
- NEIGH_VAR(p, PROXY_DELAY));
+ int delay = READ_ONCE(NEIGH_VAR(p, PROXY_DELAY));
+
+ if (unlikely(delay <= 0))
+ sched_next = now;
+ else
+ sched_next = now + (prandom_u32() % delay);
if (tbl->proxy_queue.qlen > NEIGH_VAR(p, PROXY_QLEN)) {
kfree_skb(skb);
--
2.20.1 (Apple Git-117)
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